Semiconducting polymer nanoparticles as photoacoustic molecular imaging probes

A method of molecular imaging, comprising the steps of:

• (a) delivering to a human or non-human subject a pharmaceutically acceptable composition comprising a plurality of nanoparticles comprising an organic photovoltaic semiconductor polymer, and a phospholipid a reactive oxygen species (ROS)-inactivated fluorophore, wherein the semiconductor polymer is characterized as near-infra red absorbing and generating a first detectable photoacoustic signal spectrum when irradiated by an incident activation energy;
• (b) irradiating the human or non-human subject with a first incident energy having a first wavelength and generating a first photoacoustic signal;
• (c) irradiating the human or non-human subject with a second incident energy having a second wavelength and generating a second photoacoustic signal;
• (d) determining the intensities of the first and the second photoacoustic signals;
• (e) determining a first ratio of the intensities of the first and the second photoacoustic signals;
• (f) comparing said first ratio with a second ratio determined from the nanoparticles before delivery to the human or non-human subject, whereby a difference in said first and second ratios indicates RONS degradation of the nanoparticles in the subject;
• and
• (g) generating a ratiometric image indicating the difference in said first and second ratios relative to an image of the subject.